Method of controlling lost circulation in well drilling

ABSTRACT

Loss of drilling fluid into a subterranean formation penetrated in the drilling of a well is controlled by addition to the drilling fluid of a lost circulation material comprising petroleum coke.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the drilling of wells, and more particularlyto controlling or stopping the loss of drilling fluid into subterraneanformations penetrated by the wells.

In the drilling of a well into the earth by rotary drilling techniques,conventionally a drilling fluid is circulated from the surface of theearth down a drill string having a drill bit on the lower end thereofand through ports provided in the drill bit to the well bottom andthence back to the surface through the annulus formed about the drillstring. Commonly, drilling fluids are employed that are either oil orwater base. These fluids are treated to provide desired rheologicalproperties which make the fluids particularly useful in the drilling ofwells.

A problem often encountered in the drilling of a well is the loss ofunacceptably large amounts of drilling fluid into subterraneanformations penetrated by the well. This problem is often referred togenerally as "lost circulation," and the formations into which thedrilling fluid is lost are often referred to as "lost circulation zones"or "thief zones". Various causes may be responsible for the lostcirculation encountered in the drilling of a well. For example, aformation penetrated by the well may exhibit unusually high permeabilityor may contain fractures or crevices therein. In addition, a formationmay simply not be sufficiently competent to support the hydrostaticpressure applied by the drilling fluid and may break down under thishydrostatic pressure and allow the drilling fluid to flow thereinto.

2. The Prior Art

Numerous techniques have been developed to control lost circulation. Onecommon technique involves increasing the viscosity of the drilling fluidto increase its resistance to flow into the formation. Another techniqueinvolves the addition of bulk material, such as cottonseed hulls,sawdust, or ground walnut shells, to the drilling fluid In addition,asphaltic materials including gilsonite have been added to both waterbase and oil base fluids to prevent the loss of drilling fluid from thewell into surrounding formations. For example, in U.S. Pat. No.2,773,670 to Miller, there is taught a method of stopping lostcirculation by adding asphaltic material to drilling fluids. Thesematerials are added to the drilling fluid in the form of discreteparticles and are suspended as such in the fluid where they are carrieddown the drill pipe and thence via the annulus between the pipe and thewell bore to the lost circulation zone. Upon reaching the lostcirculation zone, due in part at least to the elevated temperatures andpressures found in the well, the asphalt particles attach themselves tothe formation and are fused or bonded to one another and to theformation structure to form an effective seal against the passage ofdrilling fluid into the formation.

The use of gilsonite in suitable granular form in an aqueous carrierliquid for stopping lost circulation is taught in U.S. Pat. No.2,812,161 to Mayhew. The granules of gilsonite are simply mixed with aportion of aqueous drilling mud and pumped into the well bore so thatthe mud will carry the gilsonite granules to the leaking strata andforce them into the crevices therein. In accordance with Mayhew, theeffective concentration of the granular gilsonite in the aqueous liquidcarrier ranges from as little as 10 pounds up to 50 pounds per barrel ofthe mixture for most common cases of lost circulation, and for severeconditions this concentration may be increased to as much as 100 poundsper barrel.

In U.S. Pat. No. 2,573,690 to Cardwell et al. there is described amethod of treating earth formations wherein a filler, which is a solidsubstance in granular form in two ranges of particle size, one beingcoarse and corresponding in size to the channel fissures and cracks, theother comparatively fine and corresponding in size to the particles ofthe formation to be consolidated, is used in conjunction with an earthconsolidating resin-forming liquid mixture. Among those substancessuggested as filler are walnut shells, pecan shells, coconut shells, andgilsonite.

Other granular materials used in the prevention of loss of fluid intoformations include coal and coke. For example, in U.S. Pat. No.2,650,195 to Cardwell et al., there is disclosed a method of preventingthe loss of fluid into formations by providing a cohesive resinouscoating upon filterable inert solid particles which are added to thefluid so as to form a filter cake of self-bonding particles when a thiefzone is encountered. Various filler materials which are disclosedinclude coke, coal, cinders, and nut shells. The "coke" which has beenused in these prior art techniques has been derived from coal bysubjecting coking coal to partial oxidation in coke ovens.

U.S. Pat. No. 3,788,406 to Messenger describes addition of anemulsifying agent and a large amount of ground coal or asphalticoil-wettable granular particles to control lost circulation.

SUMMARY OF THE INVENTION

This invention is directed to a method of controlling drilling fluidloss by adding particulate petroleum coke to the drilling fluid. Themechanics of the method of this invention do not differ appreciably frompreviously known methods for controlling drilling fluid loss or "lostcirculation", but it has been found that particulate petroleum cokehaving an appropriate size distribution and in appropriate concentrationis a particularly effective lost circulation material.

The present invention provides a method of controlling severe lostcirculation problems which may be encountered when drilling a well witheither oil base or water base drilling fluids. This method hasparticular application in controlling lost circulation when drillingwith oil base fluids, and is hereinafter described with reference to usewith such fluids. It is to be understood, however, that it is alsoapplicable for use in controlling lost circulation when drilling withwater base fluids.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The lost circulation material in accordance with this invention ispetroleum coke. Petroleum coke is produced either by the delayed cokingprocess, in which a residual oil is heated and fed to a coking drumwhere the oil cracks to produce vapors and coke in a semi-batch typeprocess, or by the fluidized bed process, in which small coke particlesare produced and recovered in a continuous process. The preferredmaterial is delayed petroleum coke, and more preferably. delayedpetroleum "shot" coke. Shot coke is produced generally by operating adelayed coker at slightly more severe than normal conditions. The shotcoke is formed as clusters of small spherical coke particles. Delayedcoke which does not have the characteristics of shot coke is typically asolid amorphous mass composed largely of carbon. One preferred form ofcoke for use in accordance with the invention is calcined delayedpetroleum coke. Calcination reduces the amount of volatile hydrocarbonsin the coke and minimizes the chances of the coke reacting withadditives in the drilling fluid. Inclusion of from about 1 up to about 5percent by weight of finely divided fibrous particles such as oilwettable cellulosic particles often improves performance, particularlywhen the drilling fluid is an oil base fluid.

The size distribution of the coke particles should be such that thelarger particles do not plug the openings in the drill bit, mud motor orother downhole equipment through which the drilling fluid is pumped,with the bulk of the particles being distributed over a size rangesuitable for blocking openings in the formation with a relatively thinlayer of coke particles.

Operable and preferred size distributions for the coke particles aretabulated below:

    ______________________________________                                        Size Distribution Table                                                       Sieve Size                                                                    Range (Tyler                                                                           Particle     Allowable  Preferred                                    Mesh Sizes)                                                                            Diameter (mm)                                                                              Wt % Ranges                                                                              Wt % Ranges                                  ______________________________________                                         +6                    0         0                                             6 × 10                                                                          1.7-3.4      <5         0                                             10 × 32*                                                                        0.5-1.7      20-40       30-40*                                      32 × 60                                                                          0.25-0.5     15-40      20-30                                         60 × 100                                                                        0.15-0.25    10-30      10-20                                        100 × 200                                                                        0.07-0.15     5-30       5-10                                        -200     <0.07        <5         <5                                           *Preferred breakdown of 10 × 32 mesh range is as follows:               Tyler Mesh    Wt % Range                                                      10 × 14 10-20                                                           14 × 20 10-20                                                           20 × 32 10-20                                                           ______________________________________                                    

Delayed petroleum coke has a particle density of about 1.8-2.0 gm/cc.and thus moves with the drilling fluid without a tendency to settle outor float unduly.

Delayed petroleum coke is particularly useful when the drilling fluid isan oil base fluid, because it is an oil-wettable material, and can beadded to oil base fluids in very high concentrations withoutsignificantly affecting the rheology of the fluid. Loadings of 300 tomore than 400 pounds of coke per barrel are possible while stillmaintaining a pumpable mud. Other characteristics of petroleum coke thatmake it especially attractive as a lost circulation material are its lowporosity and resulting low surface area, its non-swelling property incontact with drilling fluids, its low reactivity or absorptivity withchemicals in the drilling fluid. its low solubility in oil base mud, andits high particle strength and integrity. Calcined delayed petroleumshot coke is especially desirable.

The petroleum coke is added to the drilling fluid in the same manner asconventional lost circulation materials are added.

Experiments were carried out to compare the performance of particulatepetroleum coke against several commercial additives for seepage and lostcirculation control. The evaluation included formation damage, sealefficiency, abrasion and mud stability testing. The seal efficiency testused filtration discs having permeabilities up to 200 darcies.

In these experiments, particulate petroleum coke did not contribute toformation damage of Berea sandstone cores. No formation damage wasevident in a mud system containing mica. Substantial damage was apparentwith treated cellulosic fiber in a whole mud after aging.

Petroleum coke with proper size distribution at concentrations of 40 to60 pounds per barrel in low, medium and high weight water base and oilbase muds was effective in sealing a wide range of filter media. Smallerparticle size petroleum coke was not as effective. Treated cellulosicfiber as the primary lost circulation material was ineffective in manytests because of the sensitivity of muds containing it to the pore sizeof the filter media and to the solids concentration of the base mud. Asa result filter cakes up to eight centimeters thick were formed in somesystems. Mica was effective in sealing the test media except in oil basemuds where high concentrations of mica were required to seal the discs.Excessive mica destabilized the emulsion in oil muds.

The abrasiveness test results for petroleum coke in a mud werecomparable to those obtained with mica.

The tests showed that petroleum coke would not affect the baseproperties of an oil mud, and was equal to or better than variousconcentrations or blends of mica, nut hulls, or treated cellulosic fiberto seal porous substrates.

In the following tests, the term "Fann Dial Reading" refers to theoutput reading of a particular viscometer, which reading may beconverted by a proper constant to give a value for viscosity. In actualpractice, it is conventional to simply report the Fann Dial readingdirectly A higher number represents a higher viscosity. The term"emulsion stability" or "E.S." refers to the voltage required to beimposed on a pair of electrodes to obtain conductivity when theelectrodes are immersed in an emulsion. A high number represents highemulsion stability.

When the term "coke" or "petroleum coke" appears in the followingtables, it refers to delayed petroleum coke having a size distributionapproximately as follows:

    ______________________________________                                        Size - U.S. Sieve Series                                                                      Weight Percent Particles                                      ______________________________________                                         +10            13                                                            10 × 20   32                                                            20 × 60   31                                                             60 × 100  8                                                            100 × 200  9                                                            -200             7                                                            ______________________________________                                    

When the term "finely divided coke" appears, it refers to calcineddelayed petroleum coke having a size distribution approximately asfollows:

    ______________________________________                                        Size - U.S. Sieve Series                                                                      Weight Percent Particles                                      ______________________________________                                        10 × 20    5                                                            20 × 30    5                                                            30 × 60   28                                                             60 × 100 25                                                            100 × 200 24                                                            -200            13                                                            ______________________________________                                    

EXAMPLE 1

In this example, formation damage is determined by measuring thepermeability of a sample which had been vacuum saturated with connatewater to a fluid flowing "formation-to-borehole" (initial permeability),treating the sample with an experimental fluid flowing"borehole-to-formation" (mud-off, filtrate, acidize, etc.) andremeasuring the permeability to the fluid "formation-to-borehole"(return permeability). Results are generally reported as percent returnpermeability calculated as follows: ##EQU1##

The following procedure outlines the test method used:

1. The length and diameter of a Berea sandstone core having a nitrogenpermeability of approximately 200 md was measured and recorded.

2. The core was saturated with simulation formation water under vacuumfor 24 hours.

3. The core was placed in a Hassler cell.

4. A confining pressure of 1000 psi was placed on the sleeve holding thecore via the hydraulic pump and maintained while heating the Hasslercell to 200° F.

5. The initial permeability to oil was determined by pushing oil throughthe core and measuring the pressure and volume of oil with respect totime. The time and volume of oil were measured until a steady state hadbeen achieved.

6. The "borehole" face of the core was either subjected to the mudfiltrate by applying a differential pressure to the cell to flow ameasured volume of filtrate through the core (30 cm³) or subjected towhole mud for two hours at a differential pressure of 1000 psi.

7. The core was held static for one hour with no differential pressureand the return permeability was then determined by repeating step numberfive.

The results of the formation damage tests are presented in Tables 1through 4. The results of using the filtrate of a mud with and withoutpetroleum coke are presented in Table 1. These data indicate thatpetroleum coke does not contain oil soluble components that aredetrimental to the flow of mineral oil through the Berea sandstoneformation. The low return permeability of the control system indicatesthat an excess of emulsifier was present in the mud. This was deliberatein the design of the experiment in order to demonstrate the effect ofexcess emulsifier on formation damage and determine the interaction ofemulsifier and petroleum coke. The higher percent of return permeabilityof the mud with petroleum coke indicates that the coke can absorb excessemulsifier from the oil phase. This suggests that additional wettingagent such as a polyamide emulsifier should be a supplemental additive.The before and after hot rolling results reveal that no degradationproducts of the emulsifiers or the coke that impact on the oilpermeability of the sandstone are created at 250° F.

Table 2 shows the effects on return permeability of various whole mudsThis system was designed with high filtration for observation of theeffects of petroleum coke. No adverse affects were noted.

Tables 3 and 4 are of an oil base mud formulated for optimum performancethat was tested with two other common lost circulation materials,treated cellulosic fiber and mica. No damage was noted with the mica butsignificant damage was noted with the fiber. The higher than 100% returnpermeability effect may be due to a further reduction in residual watercontent of the core from the back flow of mud filtrate. Oil from the mudfiltrate releases some trapped residual connate water increasing thepermeability of subsequent oil flows. Several potential sources of thedamage exist. The fiber may have plugged the pore throats as fibers werevisible on the surface of the core at the conclusion of the test. Thefibers may have taken up some water and allowed water to enter the core.This is suggested due to the increased rate of separation of the oilfrom the mud noted at room temperature after hot rolling and the loweremulsion stability values. It should be noted that no free water wasdetected in the 300° F filtration test. This mud separation phenomenonmay account for the mushy filter cake on the core sample. The organicmaterial used to make the fiber oil-dispersible may have come off thefiber during hot rolling and been in solution in the oil phase. Thisorganic material could easily change the wettability of the core.

The rheological and filtration control properties of the muds in Tables3 and 4 were obtained to demonstrate the effects the various additiveswould have on the base muds. Only the petroleum coke had a negligibleeffect on the base mud. The coke was screened out of the mud to preventparticulate interference just prior to running the rheologicalproperties, and the test mud shows little change from the aged base mud.

                  TABLE 1                                                         ______________________________________                                        FORMATION DAMAGE OF OIL MUD FILTRATE                                          FROM MUDS WITH AND WITHOUT PETROLEUM                                          COKE AND BEFORE AND AFTER AGING                                               ______________________________________                                        Mud Composition                                                               85:15 Oil-Water Ratio, 9 Lb/Gal Oil Base Mud                                  Diesel, cm.sup.3       284            284                                     Polyamide Emulsifier,  5              5                                       cm.sup.3                                                                      30% CaCl.sub.2 solution, cm.sup.3                                                                    49             49                                      Organophilic Clay, g   3.5            3.5                                     Oxidized Tall Oil, cm.sup.3                                                                          1              1                                       Lime, g                1              1                                       Barite, g              76             76                                      Petroleum Coke, g      --             60                                      Rheological and Filtration Control Properties at 120° F.               Hrs. Hot-rolled @                                                                           0        16       0     16                                      250° F.                                                                Fann Dial Reading @                                                           600 rpm       31       24       Both are thin                                 300 rpm       18       14       and                                           200 rpm       12       10       flowable                                      100 rpm       8        6                                                       6 rpm        3        3                                                       3 rpm        3        3                                                      Plastic Viscosity, cP                                                                       13       10                                                     Yield Point, lbf/100 ft.sup.2                                                               5        4                                                      10 Sec Gel, lbf/100 ft.sup.2                                                                4        3                                                      10 Min Gel, lbf/100 ft.sup.2                                                                5        5                                                      E.S., volts   1500     1280     810   1000                                    Filtration Control -                                                                        11.2     13.6     10.4  13.6                                    300° F./500 psi,                                                       cm.sup.3 in 30 min                                                            Cake Thickness                                                                              3        3        3     3                                       (32nd in)                                                                     Formation Damage of Filtrates (Berea)                                         Return Permeability @                                                                       50       45       82    90                                      200° F.                                                                Percent                                                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        FORMATION DAMAGE OF OIL MUD                                                   WITH AND WITHOUT PETROLEUM                                                    COKE AFTER AGING                                                              ______________________________________                                        Mud Composition                                                               85:15 Oil-Water Ratio, 16 Lb/Gal Oil Base Mud                                 Diesel, cm.sup.3        200           200                                     Polyamide Emulsifier, cm.sup.3                                                                        3.5           3.5                                     30% CaCl.sub.2 solution, cm.sup.3                                                                     36            36                                      Organophilic Clay, g    2             2                                       Oxidized Tall Oil, cm.sup.3                                                                           5             5                                       Lime, g                 4             4                                       Barite, g               445           445                                     Amine Treated Lignite, g                                                                              5             5                                       Petroleum Coke, g       --            65                                      Rheological and Filtration Control Properties at 120° F.               Hrs. Hot-rolled @ 250° F.                                                               0      16         0  16                                      Fann Dial Reading @                                                           600 rpm         78      76       Both are thin                                300 rpm         45      43       and                                          200 rpm         34      32       flowable                                     100 rpm         23      21                                                     6 rpm          10      8                                                      3 rpm           9      7                                                     Plastic Viscosity, cP                                                                         33      33                                                    Yield Point, lbf/100 ft.sup.2                                                                 12      10                                                    10 Sec Gel, lbf/100 ft.sup.2                                                                  11      9                                                     10 Min Gel, lbf/100 ft.sup.2                                                                  14      11                                                    E.S., volts     1980    1060     2000 1220                                    Filtration Control -                                                                          --      36.2     --   22.4                                    300° F./500 psi,                                                       cm.sup.3 in 30 min                                                            Cake Thickness (32nd in)                                                                      --      7        --   8                                       Formation Damage of Whole Mud (Berea)                                         Return Permeability @                                                                         --      56       --   71                                      200° F.                                                                Percent                                                                       ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        FORMATION DAMAGE OF OIL BASE                                                  MUD WITH AND WITHOUT PETROLEUM                                                COKE AFTER AGING                                                              ______________________________________                                        Mud Composition                                                               85:15 Oil-Water Ratio, 16 Lb/Gal Oil Base Mud                                 Oil, cm.sup.3           200           200                                     Polyamide Emulsifier, cm.sup.3                                                                        5             5                                       30% CaCl.sub.2 solution, cm.sup.3                                                                     35            35                                      Organophilic Clay, g    6.5           6.5                                     Oxidized Tall Oil, cm.sup.3                                                                           5             5                                       Lime, g                 4             4                                       Barite, g               449           449                                     Amine Treated Lignite, g                                                                              15            15                                      Petroleum Coke, g       --            40                                      Rheological and Filtration Control Properties at 120° F.               Hrs. Hot-rolled @ 250° F.                                                             0        16         0  16*                                     Fann Dial Reading @                                                           600 rpm        132      89            96                                      300 rpm        77       53            56                                      200 rpm        56       41            42                                      100 rpm        34       27            27                                       6 rpm         9        9             8                                        3 rpm         8        8             7                                       Plastic Viscosity, cP                                                                        55       36            40                                      Yield Point, lbf/100 ft.sup.2                                                                22       17            16                                      10 Sec Gel, lbf/100 ft.sup. 2                                                                10       10            10                                      10 Min Gel, lbf/100 ft.sup.2                                                                 18       13            11                                      E.S., volts    1560     1720     1520 1460                                    Filtration Control -                                                                         3.2      2.0      --   2.2                                     300° F./500 psi,                                                       cm.sup.3 in 30 min                                                            Cake Thickness 3        2        --   2                                       (32nd in)                                                                     Formation Damage of Whole Mud (Berea)                                         Return Permeability @                                                                        --       113      --   107                                     200° F.                                                                Percent                                                                       ______________________________________                                         *Petroleum coke screened out just prior to measuring rheology.           

                  TABLE 4                                                         ______________________________________                                        FORMATION DAMAGE OF OIL BASE MUD                                              WITH CELLULOSIC FIBER AND MICA                                                AFTER AGING                                                                   ______________________________________                                        Mud Composition                                                               85:15 Oil-Water Ratio, 16 Lb/Gal Oil Base Mud                                 Oil, cm.sup.3             200          200                                    Polyamide Emulsifier, cm.sup.3                                                                          5            5                                      30% CaCl.sub.2 solution, cm.sup.3                                                                       35           35                                     Organophilic Clay, g      6.5          6.5                                    Oxidized Tall Oil, cm.sup.3                                                                             5            5                                      Lime, g                   4            4                                      Barite, g                 449          449                                    Amine Treated Lignite, g  15           15                                     Cellulosic Fiber, g       30           --                                     Mica, g                   --           30                                     Rheological and Filtration Control Properties at 120° F.               Hrs. Hot-rolled @ 250° F.                                                                 0      16       0   16                                     Fann Dial Reading @                                                           600 rpm           263     167     244  195                                    300 rpm           147     98      143  114                                    200 rpm           106     71      106  84                                     100 rpm            62     42      65   52                                      6 rpm             11     11      20   14                                      3 rpm             8      8       18   12                                     Plastic Viscosity, cP                                                                           116     69      99   81                                     Yield Point, lbf/100 ft.sup.2                                                                    31     29      44   33                                     10 Sec Gel, lbf/100 ft.sup.2                                                                     9      10      24   14                                     10 Min Gel, lbf/100 ft.sup.2                                                                     24     12      35   17                                     E.S., volts       1500    160     630  720                                    Filtration Control -                                                                            --      3.6     --   3.2                                    300° F./500 psi,                                                       cm.sup.3 in 30 min                                                            Cake Thickness (32nd in)                                                                        --      3       --   3                                       *Petroleum coke screened out just prior to measuring rheology.           

    Formation Damage of Whole Mud (Berea)                                         Return Permeability @ 200° F.                                                            --      43*     --   112                                    Percent                                                                       ______________________________________                                         *66% after physical removal of filter cake.                              

EXAMPLE II

This test was designed to determine the seal efficiency of petroleumcoke compared to commercial lost circulation materials. The testequipment involved was a modified high temperature, high pressurefiltration unit. The cell was modified to accept 1/4 inch thick porousfilter media having permeabilities of from 2 to 200 darcys. Samples ofbase mud were mixed with the additive under test and the ability of themud to seal the disc was determined. This was done by applying 100 psito the cell and measuring the spurt loss volume and elapsed time or thetime for the cell to blow dry. If the material sealed the disc. thepressure was increased to 500 psi for thirty minutes. The total volumeof filtrate and filter cake structure was noted.

Petroleum coke was effective in all water and oil mud systems evaluatedat a concentration level of 40 to 60 lb/bbl. No thick filter cakes wereobserved and little change was noted in the mud properties as indicatedby the emulsion stability. The particle size distribution is critical toperformance as indicated by the results in Table 17 for finely dividedpetroleum coke. Petroleum coke (XY) was a sample of material from awarehouse location that was slightly finer in particle size than theother petroleum coke. The limited testing of the finer petroleum cokeindicated that it would seal the discs with a porosity of 200 darcys.This may have been a matter of concentration in that a highconcentration of large particles was present to seal whereas a lowerlevel of finer coke may not have sealed the disc as effectively.

Mica was effective but had one shortcoming. When using highconcentrations to seal the more porous discs, the mica began todestabilize the mud as indicated by high rheological properties and lowemulsion stability values. This is shown in Table 7. This limitation canbe overcome by increasing the concentration of wetting agent oremulsifier but adds to mud treatment cost. The problem is caused by thehigh surface area wetting requirement of mica in oil muds. The use ofhigh concentrations of mica in water muds would not pose this problem.

The results for treated cellulosic fiber in Tables 5, 6 and 21 show thatit was very sensitive to the concentration of solids and pore size ofthe test media. The structure of the filter cakes was very distinct whenthe fiber and mud did not form a seal. A very porous mat structure up tothree inches was formed. This same type of mat structure was formed withthe fiber/coke combinations tested and reported in Table 8. These filtercakes had coke dispersed uniformly throughout the mat structure.

Physical blends of petroleum coke and fiber were tested and performancewas comparable to the use of unadulterated coke. A comparison of a fiberand nut hulls blend was made to fiber and coke in Tables 6, 7 and 11.The blends were equivalent in performance. Studies have shown that thenut hulls alone are not effective and they can contribute to substantialdepletion of emulsifier and wetting agents when used in oil muds. Thesedata indicate that petroleum coke seals porous media in laboratory testsas well as a commonly used fiber/nut hull blend but does not adverselyaffect the properties of the base oil mud like the blend does.

                  TABLE 5                                                         ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                  A          B      C      D     E    F    G    H                               ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 9 Lb/Gal Oil Base Mud                        Base Mud,                                                                              350    350    350  350   350  350 350   350                          cm.sup.3                                                                      Coke, g  20     40     60   60    60   60  --   --                            Fiber, g                                                                              --     --     --   --    --   --    40   60                           Disc     200    200    200  100   40    5  200   200                          Perme-                                                                        ability -                                                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume   17      6      0     0.4                                                                                0    0   0     0                           cm.sup.3                                                                      Time, sec                                                                              11     10      0    2     0    0   0     0                           Blow Dry,                                                                             --     --     --   --    --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume,  46     11      6    8     5    2   40   54                           cm.sup.3                                                                      Blow Dry,                                                                             --     --     --   --    --   --   --   --                            sec                                                                           Cake,     6      3      5    5     4    5   24  *                             32nd in.                                                                      Fann Dial Readings and Emulsion Stability                                     600 rpm                                     59   67                           300 rpm                                     32   39                           200 rpm                                     22   29                           100 rpm                                     12   19                            6 rpm                                      5     6                            3 rpm                                      5     6                           E.S., volts                                                                           1650   1610   1650 1650  1650 1650 720  1260                          ______________________________________                                         *The filter cake disintegrated during disassembly of the cell.           

                  TABLE 6                                                         ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                         A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 9 Lb/Gal Oil Base Mud                        Base Mud,                                                                               350    350    350 350   350  350  350  350                          cm.sup.3                                                                      Coke, g  --     --     --   --    30   30   30   30                           Fiber, g  60     60     60   40   10   10   10   10                           Disc Perme-                                                                              5     40     100 100    5   40   100  200                          ability -                                                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                        220    200    210  3     0    0    0    1                           Time, sec                                                                              --     --     --    7     0    0    0    3                           Blow Dry,                                                                               37     35      48 --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                       --     --     --    57    0    2    3    3                           Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake,     88     88     88   12    1    1    1    2                           32nd in.                                                                      Fann Dial Readings and Emulsion Stability                                     600 rpm   67     67     67   59                                               300 rpm   39     39     39   32                                               200 rpm   29     29     29   22                                               100 rpm   19     19     19   12                                                6 rpm     6      6      6   5                                                 3 rpm     6      6      6   5                                                E.S., volts                                                                            1260   1260   1260 720  1570 1570 1570 1570                          ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                         A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 9 Lb/Gal Oil Base Mud                        Base Mud,                                                                              350     350    350  350 350   350  350  350                          cm.sup.3                                                                      Coke, g  --     --     --   --   --   --   --   --                            Fiber, g --     --     --   --   --    10   10   10                           Mica, g   60     30     30   30   40  --   --   --                            Nut Hulls, g                                                                           --     --     --   --   --    30   30   30                           Disc Perme-                                                                            200     200    100   5  200   40   100  200                          ability -                                                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                        0       0      0    1  154    0     1   1                           Time, sec                                                                               0       0      0    3  120    0    4    2                           Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                        10     40     12   19  162    5   11    7                           Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake,     7     *        5    6  *      3    3    3                           32nd in.                                                                      Fann Dial Readings and Emulsion Stability                                     600 rpm  160     48     48   48   48                                          300 rpm  108     28     28   28   29                                          200 rpm   86     21     21   21   22                                          100 rpm   62     14     14   14   15                                           6 rpm    22      6      6    6   7                                            3 rpm    19      5      5    5   7                                           E.S., volts                                                                            200    1140   1140 1140 700  1100 1100 1100                          ______________________________________                                         *The filter cake disintegrated during disassembly of the cell.           

                  TABLE 8                                                         ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                             A     B       C       D    E                                       ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 9 Lb/Gal Oil Base Mud                        Base Mud, cm.sup.3                                                                         350     350     350   350  350                                   Coke, g      30       30     30    --   30                                    Fiber I, g   --      --      --    40   30                                    Fiber II, g   2       5       2    --   --                                    Disc Permeability -                                                                        200     200     40     2   200                                   Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                            3       7      10     1   0                                     Time, sec    10       20      7     3   0                                     Blow Dry, sec                                                                              --      --      --    --   --                                    Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                           230     230     22    12   3                                     Blow Dry, sec                                                                              40      140     --    --   --                                    Cake, 32nd in.                                                                             56       84      6     7   1                                     Fann Dial Readings and Emulsion Stability                                     600 rpm                            59                                         300 rpm                            32                                         200 rpm                            22                                         100 rpm                            12                                          6 rpm                              5                                          3 rpm                              5                                         E.S., volts  1320    1000    1320  720                                        ______________________________________                                         NOTE: A & C were thin and pumpable, B was lumpy and not pumpable.        

                  TABLE 9                                                         ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                  A         B      C       D    E    F    G     H                               ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 14 Lb/Gal Oil Base Mud                       Base    350    350    350   350  350  350  350  350                           Mud,                                                                          cm.sup.3                                                                      Coke, g                                                                               20     40     60    40   60   40   40   --                            Fiber, g                                                                             --     --     --    --   --   --   --     20                           Disc    100    100    100   200  200   2   40   100                           Perme-                                                                        ability -                                                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume,                                                                                8      9       0.2                                                                                0    0    0    0      0.3                        cm.sup.3                                                                      Time,    5      4      1     0    0    0    0    1                            sec                                                                           Blow   --     --     --    --   --   --   --    --                            Dry,                                                                          sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume,                                                                               17     18      7     2    2    5     0.6                                                                               34                           cm.sup.3                                                                      Blow   --     --     --    --   --   --   --    --                            Dry,                                                                          sec                                                                           Cake,    3      4      3     2    2    2    2    6                            32nd in.                                                                      Fann Dial Readings and Emulsion Stability                                     600 rpm                                          82                           300 rpm                                          53                           200 rpm                                          43                           100 rpm                                          31                            6 rpm                                           16                            3 rpm                                           16                           E.S.,  1470   1440   1460  1440 1460 1440 1440  720                           volts                                                                         ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                         A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio, 14 Lb/Gal Oil Base Mud                       Base Mud,                                                                              350    350    350  350  350  350  350  350                           cm.sup.3                                                                      Coke, g  --     --     --   --   --   --   --   --                            Fiber, g  40     40     40   40  --   --   --   --                            Mica, g  --     --     --   --    40   60   30   30                           Disc Perme-                                                                            100    200     40   2   100  100  100  200                           ability -                                                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                        0      1      0    0    0    0    0    14                           Time, sec                                                                               0      2      0    0    0    0    0    23                           Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                        22     19     28     0.6                                                                              25   33   9    25                           Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake,     13     6      18   4    13   28   6    2                            32nd in.                                                                      Fann Dial Readings and Emulsion Stability                                     600 rpm  150    150    150  150   97  148   66   66                           300 rpm  104    104    104  104   57   87   41   41                           200 rpm   87     87     87   87   43   71   31   31                           100 rpm   63     63     63   63   30   49   22   22                            6 rpm    32     32     32   32   14   19   11   11                            3 rpm    31     31     31   31   13   17   10   10                           E.S., volts                                                                            260    260    260  260  360  160  640  640                           ______________________________________                                    

                                      TABLE 11                                    __________________________________________________________________________    EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                           A  B    C    D    E    F  G    H                                     __________________________________________________________________________    Base Mud: 85:15 Oil-Water Ratio, 14 Lb/Gal Oil Base Mud                       Base Mud, cm.sup.3                                                                      350                                                                              350  350  350  350  350                                                                              350  350                                  Coke, g   30                                                                               30   30   30  --   -- --   --                                    Fiber, g  10                                                                               10   10   10   10   10                                                                               10   10                                   Nut Hulls, g                                                                           -- --   --   --    30   30                                                                               30   30                                   Disc Permeability -                                                                      2                                                                               40   100  200   5   40                                                                               100  200                                  Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                         0                                                                                0     0.1                                                                               0    0    0                                                                                 0.5                                                                                0.2                                Time, sec                                                                                0                                                                                0    2    0    0    0                                                                                1   12                                   Blow Dry, sec                                                                          -- --   --   --   --   -- --   --                                    Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                         1                                                                                 0.5                                                                               3     0.4                                                                                0.2                                                                               3                                                                               12    5                                   Blow Dry, sec                                                                          -- --   --   --   --   -- --   --                                    Cake, 32nd in.                                                                           2                                                                                2    3    2    2    2                                                                                3    5                                   Fann Dial Readings and Emulsion Stability                                     600 rpm                                                                       300 rpm                                                                       200 rpm                                                                       100 rpm                                                                        6 rpm                                                                         3 rpm                                                                        E.S., volts                                                                            1680                                                                             1680 1680 1680 1600 1600                                                                             1600 1600                                  __________________________________________________________________________

                  TABLE 12                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY' OF LCM                                     MATERIAL ON FILTRATION DISCS                                                              A         B      C                                                ______________________________________                                        Base Mud: 85:15 Oil-Water Ratio. 14 Lb/Gal Oil Base Mud                       Base Mud, cm.sup.3                                                                          350         350    350                                          Coke, g        20          20    --                                           Fiber, g       20          20    --                                           Mica, g       --          --     30                                           Disc Permeability                                                                           100         200    40                                           Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                             0             0.5  0                                           Time, sec      0           10     0                                           Blow Dry, sec --          --     --                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                             13          13     9                                           Blow Dry, sec --          --     --                                           Cake, 32nd in.                                                                               7           7      6                                           Fann Dial Readings and Emulsion Stability                                     600 rpm                  59                                                   300 rpm                  37                                                   200 rpm                  29                                                   100 rpm                  20                                                    6 rpm                   10                                                    3 rpm                   10                                                   E.S., volts              460                                                  ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON DISCS                                                                    A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 16.4 Lb/Gal Field Oil Base Mud                                      Base Mud,                                                                              350    350    350  350  350  350  350  350                           cm.sup.3                                                                      Coke, g   40    40      40   40   40  --   --   --                            Fiber, g --     --     --   --   --    40   40   40                           Disc Permea-                                                                            5     40     100  200   5    40  100  200                           bility                                                                        Darcys   100                                                                  Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                       0      0      0    0.5  0    0    0    50                            Time, sec                                                                              0      0      0    10   0    0    0    60                            Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                       0.1    0      0    3    0    0    0    90                            Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake, 32nd                                                                             2      1      1    1    1    3    2     1                            in.                                                                           Fann Dial Readings and Emulsion Stability                                     600 rpm                               226  226  226                           300 rpm                               126  126  126                           200 rpm                                94   94   94                           100 rpm                                59   59   59                            6 rpm                                 18   18   18                            3 rpm                                 16   16   16                           E.S., volts                                                                            1300   1300   1300 1300 1300 240  240  260                           ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY 26 LCM                                      MATERIAL ON FILTRATION DISCS                                                           A     B      C      D    E    F    G                                 ______________________________________                                        Base Mud: 16.4 Lb/Gal Field Oil Base Mud                                      Base Mud, cm.sup.3                                                                       350     350    350  350  350  350  350                             Coke, g    40      --     --   --   --   --   --                              Fiber, g   --      40     --   --   --   --   --                              Mica, g    --      --     30   30   30   --   --                              Disc       40      40     40   100  200  40   100                             Permeability                                                                  Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                         0       0      0    0    300  0    0                               Time, sec  0       0      0    10   --   0    0                               Blow Dry, sec                                                                            --      --     --   --   90   --   --                              Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                         Trace   0      0    0    --   0    0                               Blow Dry, sec                                                                            --      --     --   --   --   --   --                              Cake, 32nd in.                                                                           1       1      3    2    1    3    2                               Fann Dial Readings and Emulsion Stability                                     600 rpm                   147  147  147  84   84                              300 rpm                   84   84   84   49   49                              200 rpm                   63   63   63   37   37                              100 rpm                   40   40   40   24   24                               6 rpm                    13   13   13   9    9                                3 rpm                    11   11   11   8    8                               E.S., volts                                                                              1300    240    740  740  740  1320 1320                            ______________________________________                                    

                  TABLE 15                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY 35 LCM                                      MATERIAL ON FILTRATION DISCS                                                         A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 16.4 Lb/Gal Field Oil Base Mud                                      Base Mud,                                                                              350    350    350  350  350  350  350  350                           cm.sup.3                                                                      Coke, g   30     30     30   30   30  --   --   --                            Fiber, g  10     10     10   10   10   10   10   10                           Nut Hulls, g                                                                           --     --     --   --   --    30   30   30                           Disc Pearmea-                                                                           40    100    200  200  200   40  100  200                           bility                                                                        Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                       0      0      0.3   2    2   0    0     1                            Time, sec                                                                              0      0      5    20   10   0    0    15                            Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                       0      0      1     4   3.5  0    2    4                             Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake, 32nd                                                                             1      1      1    1    1    2    2    1                             in.                                                                           Fann Dial Readings and Emulsion Stability                                     600 rpm                                                                       300 rpm                                                                       200 rpm                                                                       100 rpm                                                                        6 rpm                                                                         3 rpm                                                                        E.S., volts                                                                            1350   1350   1350 1350 1350 1280 1280 1280                          ______________________________________                                    

                  TABLE 16                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                            A       B         C        D                                        ______________________________________                                                  BASE MUD:                                                                     16.4 Lb/Gal   9 Lb/Gal                                                        Field Oil Base Mud                                                                          Oil Base Mud                                          Base Mud, cm.sup.3                                                                        350       350       350    350                                    Coke, g     38.8      38.8      58.2   58.2                                   Fiber, g    1.2       1.2       1.8    1.8                                    Disc Permeability                                                                         100       200       100    200                                    Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                          0          0.5      1      0                                      Time, sec   0         10        5      0                                      Blow Dry, sec                                                                             --        --        --     --                                     Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                          0         2         6      2                                      Blow Dry, sec                                                                             --        --        --     --                                     Cake, 32nd in.                                                                            1         1         2      2                                      Fann Dial Readings and Emulsion Stability                                     600 rpm                                                                       300 rpm                                                                       200 rpm                                                                       100 rpm                                                                        6 rpm                                                                         3 rpm                                                                        E.S., volts 1520      1520      880    880                                    ______________________________________                                    

                  TABLE 17                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                             A      B        C        D                                         ______________________________________                                        Base Mud: 9 lb/gal Oil Base Mud                                               Base Mud, cm.sup.3                                                                         350      350      350    350                                     Finely Divided Coke, g                                                                     60       60       --     --                                      Coke, g      --       --       60     60                                      Disc Permeability                                                                          40       200      40     200                                     Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                           0        3.5      0      0                                       Time, sec    0        20       0      0                                       Blow Dry, sec                                                                              --       --       --     --                                      Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                           1        53       2      1                                       Blow Dry, sec                                                                              --       --       --     --                                      Cake, 32nd in.                                                                             2         3       3      2                                       ______________________________________                                    

                  TABLE 18                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                            A    B      C      D    E    F    G                                 ______________________________________                                        Base Mud: 12 Lb/Gal Sea Water Polymer Mud                                     Base Mud, cm.sup.3                                                                        350    350    350  350  350  350  350                             Coke, g     40     40     40   40   --   --   --                              Fiber, g    --     --     --   --   20   40   40                              Disc Permeability                                                                         5      40     100  200  100  100  200                             Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                          0      0      0.3  0.5  2    0    6.5                             Time, sec   0      0      2    3    10   0    5                               Blow Dry, sec                                                                             --     --     --   --   --   --   --                              Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                          0.5    4      5    3    6    5    40                              Blow Dry, sec                                                                             --     --     --   --   --   --   --                              Cake, 32nd in.                                                                            3      3      2    2    2    4    7                               Fann Dial Readings and Emulsion Stability                                     600 rpm                 116    171    171                                     300 rpm                 77     114    114                                     200 rpm                 60     91     91                                      100 rpm                 40     61     61                                       6 rpm                  9      16     16                                       3 rpm                  7      12     12                                      ______________________________________                                    

                  TABLE 19                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                               A    B         C      D                                          ______________________________________                                        Base Mud: 12 Lb/Gal Sea Water Polymer Mud                                     Base Mud, cm.sup.3                                                                           350    350       350  350                                      Mica, g        40     40        40   --                                       Disc Permeability                                                                            40     10        200  100                                      Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                              0      0         0   10                                       Time, sec       0      0         0    5                                       Blow Dry, sec  --     --        --   --                                       Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                              9      8        11   48                                       Blow Dry, sec  --     --        --   --                                       Cake, 32nd in.  7      6         7    1                                       Fann Dial Readings and Emulsion Stability                                     600 rpm        136    136       136  122                                      300 rpm        91     91        91   85                                       200 rpm        72     72        72   69                                       100 rpm        49     49        49   48                                        6 rpm         12     12        12   14                                        3 rpm          9      9         9   11                                       ______________________________________                                    

                  TABLE 20                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                         A    B      C      D    E    F    G    H                               ______________________________________                                        Base Mud: 16.4 Lb/Gal Field Oil Base Mud                                      Base Mud,                                                                              350    350    350  350  350  350  350  350                           cm.sup.3                                                                      Coke, g   40     60     60   60  --   --   --   --                            Mica, g  --     --     --   --    60   60   60   60                           Disc Permea-                                                                           100     40    100  200   5    40  100  200                           bility                                                                        Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                       8      3      0    4    0     2   2    11                            Time, sec                                                                              5      5      0    5    0    30   5    20                            Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                       17     9      2    12   11   23   20   18                            Blow Dry,                                                                              --     --     --   --   --   --   --   --                            sec                                                                           Cake, 32nd                                                                              3     6      5     9    6    8    8    2                            in.                                                                           Fann Dial Readings and Emulsion Stability                                     600 rpm                          75   75   75   75                            300 rpm                          50   50   50   50                            200 rpm                          39   39   39   39                            100 rpm                          27   27   27   27                             6 rpm                            7    7    7    7                             3 rpm                            5    5    5    5                            ______________________________________                                    

                  TABLE 21                                                        ______________________________________                                        EVALUATION OF THE SEAL EFFICIENCY OF LCM                                      MATERIAL ON FILTRATION DISCS                                                             A     B       C       D     E                                      ______________________________________                                        Base Mud: 9 Lb/Gal Sea Water Polymer Mud                                      Base Mud, cm.sup.3                                                                         350     350     350   350   350                                  Fiber, g     20      40      60    20    20                                   Disc Permeability                                                                          100     100     100   40    200                                  Darcys                                                                        Filtrate Spurt @ 100 psi                                                      Volume, cm.sup.3                                                                           55      90      185   72    75                                   Time, sec    30       5      60    60    60                                   Blow Dry, sec                                                                              --      --      --    --    --                                   Filtrate for 30 min. @ 500 psi                                                Volume, cm.sup.3                                                                           82      185     250   95    270                                  Blow Dry, sec                                                                              --      --      180   --    28                                   Cake, 32nd in.                                                                              7      40      76    10    32                                   Fann Dial Readings and Emulsion Stability                                     600 rpm      56      85      100   56    56                                   300 rpm      37      59      69    37    37                                   200 rpm      30      47      56    30    30                                   100 rpm      20      32      39    20    20                                    6 rpm        4       8      10     4     4                                    3 rpm        3       6       7     3     3                                   ______________________________________                                    

EXAMPLE III

This example was designed to measure the relative abrasiveness ofpetroleum coke and other additives. The relative abrasiveness wasdetermined with a laboratory procedure adapted from API bulletin RP 13Ifor weighting material. The test procedure uses a standard test bladeattached to a high speed mixer that shears a measured volume of base mudcontaining the additives under test. The weight loss of the blade isused to calculate the abrasiveness of the additive under test. Theprocedure outlined below varied from the test for weighting material inthat only one barrel equivalent of base mud was used and the base mudwas weighted to 12 lb/gal as opposed to 14 lb/gal. The lighter weightwas selected to limit the abrasion effects of the weighting material onthe test blade.

Table 22 contains the results of the abrasion testing. These data showthat petroleum coke and mica had nearly identical abrasion rates. Theresults for a harder and finer particle size sample of petroleum cokewere of interest. They indicate that for this type of material under thedefined test conditions, a larger particle is more abrasive than aharder particle.

The compositions of the muds used were as follows:

Sea Water Polymer Mud

    ______________________________________                                        Weighting Material:                                                                              Barite  Hematite                                           ______________________________________                                        Sea Water, bbl      0.87    0.89                                              Prehydrated gel, lb                                                                              5.0     5.0                                                NaOH, lb           1.0     1.0                                                XCD biopolymer, lb 1.0     1.0                                                ASP-700 (PHPA), lb 1.5     1.5                                                Drispac Superlo, lb                                                                              2.0     2.0                                                Pierre shale (40 mesh), lb                                                                       40.0    40.0                                               Barite, lb         178.0   --                                                 Hematite, lb       --      178.0                                              ______________________________________                                    

Oil Mud

    ______________________________________                                        Weighting Material:                                                                              Barite  Hematite                                           ______________________________________                                        Diesel, bbl         0.68    0.70                                              Oxidized Tall Oil, lb                                                                            5.0     5.0                                                Lime, lb           4.0     4.0                                                Polyamide Emulsifier, lb                                                                         3.0     3.0                                                30% CaCl.sub.2 soln., bbl                                                                         0.17    0.18                                              Organophilic Clay, lb                                                                            3.0     3.0                                                Barite, lb         228.0   --                                                 Hematite, lb       --      218.0                                              ______________________________________                                    

A model 936 Hamilton Beach mixer equipped with a Waring Blender blade,Part No. 003540, was used in the test method described below:

1. Exactly 350 cm³ of base mud was measured out for each test. The basemud was tested either neat or with 60 g of the additive under test. Thematerials evaluated in the base mud were mixed into the mud with aspatula to eliminate degradation prior to testing.

2. A new test blade was weighed to the nearest 0.1 mg and installed onthe mixer.

3. The mixing container containing the composition under test wasinstalled on the mixer with the power supply disconnected.

4. The mixer was adjusted to a rotational speed of 10,000 rpm via arheostat with the aid of the tachometer.

5. After twenty minutes the testing was terminated and the mixing bladeweighed to the nearest 0.1 mg.

The rest results are reported as milligrams lost per twenty minutes, andare given in Table 22. No rheological properties are listed for the mudscontaining petroleum coke due to the particulate interference of itbetween the rheometer bob and sleeve. However, all muds containing cokewere very thin and flowable. The funnel viscosity is not subject to thisparticle interference and was determined on a field mud containing theadditives. The results are given below as a rough comparison.

    ______________________________________                                                               Funnel Viscosity @                                     Composition            R.T., Seconds                                          ______________________________________                                        16.4 lb/gal Field Oil Mud                                                                             58                                                    Mud + Petroleum Coke @ 40 lb/bbl equiv.                                                               66                                                    Mud + Mica @ 30 lb/bbl equiv.                                                                        113                                                    Mud + Fiber @ 40 lb/bbl equiv.                                                                       167                                                    ______________________________________                                    

                  TABLE 22                                                        ______________________________________                                        ABRASION TESTING OF VARIOUS COMBINATIONS OF                                   LCM ADDITIVES AND MUD TYPES                                                                      ADDITIVE &                                                                    CONCEN-     WEIGHT                                                            TRATION     LOSS                                           MUD TYPE           lb/bbl equiv.                                                                             mg/20 min.                                     ______________________________________                                        12 lb/gal Sea Water Polymer Mud                                                                  --           7                                             with Barite                                                                   12 lb/gal Sea Water Polymer Mud                                                                  Petroleum Coke                                                                            87                                             with Barite                                                                   12 lb/gal Sea Water Polymer Mud                                                                  Finely Divided                                                                            35                                             with Barite        Petroleum Coke                                             12 lb/gal Sea Water Polymer Mud                                                                  Mica        78                                             with Barite        60                                                         12 lb/gal Sea Water Polymer Mud                                                                  --          34                                             with Hematite                                                                 12 lb/gal, 80:20 OWR, Oil Mud                                                                    --          13                                             with Barite                                                                   12 lb/gal, 80:20 OWR, Oil Mud                                                                    Petroleum Coke                                                                            47                                             with Barite                                                                   12 lb/gal, 80:20 OWR, Oil Mud                                                                    Finely Divided                                                                            18                                             with Barite        Petoleum Coke                                              12 lb/gal, 80:20 OWR, Oil Mud                                                                    Mica        40                                             with Barite        60                                                         12 lb/gal, 80:20 OWR, Oil Mud                                                                    --          88                                             with Hematite                                                                 ______________________________________                                    

We claim:
 1. In a process of drilling a well wherein a drilling fluid ispumped from the surface of the ground through a drill pipe string insaid well and back to the surface of the ground via the annulus betweensaid drill pipe string and the borehole wall of said well and whereinlost circulation of said drilling fluid is encountered, the improvementin correcting said lost circulation of said drilling fluidcomprising:(a) adding to said drilling fluid a lost circulation materialconsisting essentially of petroleum coke, said petroleum coke havingfrom 35 to 80 percent by weight particles between 10 and 60 mesh andbeing added in an amount effective to correct said lost circulation; and(b) pumping said drilling fluid containing said lost circulationmaterial into said well to contact said lost circulation zone wherebysaid zone is sealed from further lost circulation by said lostcirculation material.
 2. The process of claim 1 wherein said drillingfluid is a water base drilling fluid.
 3. The process of claim 1 whereinsaid drilling fluid is an oil base drilling fluid.
 4. The process ofclaim 1 wherein said petroleum coke is fluidized bed petroleum coke. 5.The process of claim 1 wherein said petroleum coke is delayed petroleumcoke.
 6. The process of claim 5 wherein said delayed petroleum coke isground shot coke.
 7. The process of claim 6 wherein said shot cokecontains from 50 to 70 percent by weight particles between 10 and 60mesh.
 8. The process of claim 7 wherein said coke is calcined shot coke.